JP4316511B2 - Image forming apparatus, control program for image forming apparatus, and recording medium - Google Patents

Description

  The present invention relates to an image forming apparatus that visualizes an electrostatic latent image formed on an electrostatic latent image carrier to form a visible image, and transfers the visible image while conveying the recording material to a recording material. Is.

  In an image forming apparatus, an electrostatic latent image based on image information is formed on a photosensitive member (electrostatic latent image carrier) using a writing device (writing means), and the electrostatic latent image is formed on toner (developer). To visualize the toner image (visible image). Then, the toner image is transferred from the photoconductor to a sheet of recording material using a transfer device (transfer means).

  When the transfer device is a transfer roller, the toner image is transferred by passing the sheet through a transfer nip portion where the photosensitive member and the transfer roller are pressed against each other, and the sheet (recording material) is moved by the rotational force of both members. Do it while transporting. A transfer voltage is applied to the transfer roller, and the sheet passing through the transfer nip is charged by the transfer voltage, and the toner on the photosensitive member is attracted to the sheet.

  Here, the peripheral speed of the photoconductor, the transfer roller, and the peripheral speed are set so that the transfer roller is faster than the photoconductor. As a result, the sheet is peeled off from the photoconductor while being attracted to the photoconductor and pulled by the difference in peripheral speed. This is for avoiding deterioration of print quality due to character dropout, halftone blurring, and the like due to peeling discharge generated when the sheet passes through the transfer nip portion.

  In other words, a transfer voltage is applied to the transfer roller to transfer the toner onto the paper, but it is no exaggeration to say that the portion where the transfer voltage works normally is the transfer nip portion. Therefore, the white portion of the paper in the transfer nip where toner is not attached is in a state where the paper surface (photoreceptor side) is charged to a high potential, and peels from the high potential portion on the photoconductor when leaving the transfer nip. Discharge occurs. Due to the influence of the peeling discharge, a part of the toner transferred onto the paper is reversely transferred onto the photosensitive member, resulting in the above-described deterioration in print quality.

  Further, immediately before the transfer nip portion, a paper conveyance roller called an idle roller that is rotated at substantially the same peripheral speed as the transfer roller is disposed. The idle roller is driven to rotate intermittently to align the position of the paper and the toner image on the photoreceptor. The idle roller temporarily stops when the paper is conveyed to the idle roller, stops the paper, and resumes rotational driving at the timing when the toner image on the photosensitive member passes through the transfer nip portion to transfer the paper. It is designed to be transported to the nip.

  As shown in FIGS. 9A to 9E, the leading edge of the sheet P conveyed from the idle roller 116 is slightly in the outer peripheral direction of the photosensitive member 121 with respect to the contact point of the transfer nip portion 127. It is designed to be guided toward the transfer nip portion 127 by the rotation of the photoconductor 121 after the front end of the paper contacts the photoconductor 121.

  This is because, when the leading edge of the sheet directly contacts the contact point of the transfer nip portion 127, the sheet P pulsates for a short period of time when the leading edge of the sheet is bitten into the transfer nip portion 27, and print blurring (image shift, transfer shift) occurs. This is because there is a risk of occurrence or wrinkles at the leading edge of the paper P.

  Further, as shown in FIG. 9D, a warp portion 128 of the paper P is formed immediately before the transfer nip portion 127. This is formed by making the peripheral speed of the idle roller 116 substantially the same as the peripheral speed of the transfer roller 125. By forming such a warp portion 128 immediately before the transfer nip portion 127, the sheet P is always guided to the transfer nip portion 127 while being attracted to the surface of the photosensitive member 121, and the sheet P is transferred to the transfer nip portion. It is possible to avoid a situation in which the toner is attracted to the surface of the transfer roller 125 and unnecessarily charged before reaching 27. Excessive charging of the paper causes the above-described toner reverse transfer phenomenon.

  However, such a wrinkle portion 128 acts to feed out the paper P in the transport direction by trying to become flat, so that normally the paper P does not slip due to the nip pressure of the transfer nip portion 127. That amount is set.

  In Cited Document 1, as for a paper conveyance roller disposed immediately before such a transfer nip portion, the transfer belt running speed and the registration roller regardless of changes in the registration roller performance corresponding to the paper conveyance roller over time, etc. Discloses an image forming apparatus capable of maintaining a predetermined speed difference from the recording paper conveyance speed. According to this, in the image forming apparatus in which the recording paper conveyed by the registration roller is conveyed to the image carrier for each color by the transfer belt, and the toner image on each image carrier is transferred onto the recording paper, the registration roller In addition, the rotational speed of the registration motor is driven and controlled so that the moving time of the recording leading edge and the moving time of the trailing edge of the recording paper between two sensor units arranged in parallel between the suction rollers become a predetermined value. ing.

  Further, in recent years, the particle diameter of the toner for visualizing the above-described electrostatic latent image has been reduced by increasing the resolution of image information. Conventionally, the toner particle diameter is generally in the range of 8 to 12 Φμm, but in recent years, the toner particle diameter has been changed to approximately 4 to 7 Φμm. In recent small particle size toners, even when coarse powders and fine powders are removed in the manufacturing stage, pulverization occurs due to friction during tribocharging that imparts charge to the toner, and toners of 2Φ μm or less also contribute to development. It has become like this.

  On the other hand, in an image forming apparatus, conventionally, a signal corresponding to a sheet peripheral edge assumed on the image forming apparatus side is forcibly cut with respect to an image signal given from a terminal device such as a host computer to form a margin. Things have been done.

  In other words, when an image based on the image signal given from the terminal device is to be recorded on the full sheet, the toner corresponding to the peripheral edge of the toner image on the photosensitive member is not transferred and remains on the photosensitive member. This is because the toner that has not been transferred is scattered in the main body of the apparatus, thereby degrading the image quality and inducing jamming.

  For example, Japanese Patent Application Laid-Open No. 2003-259542 discloses that the amount of the margin corresponding to each peripheral edge of the sheet is independently determined at the time of first and second image formation on the same sheet. It is described that it is different. As a result, even if an error within the tolerance range occurs, the effective utilization area for image formation can be expanded without causing the image to protrude.

Further, Patent Document 3 outputs a test pattern of a solid image with a small trailing edge margin, and after obtaining an image with a blurred trailing edge portion of the image, outputs a test pattern having a normal trailing edge margin, It describes that the trailing edge margin is adjusted to eliminate blur at the trailing edge of the image. Thereby, damage to the image carrier (photosensitive member) due to transfer charging (transfer electric field) can be prevented, and a high-quality image can be obtained.
JP 2004-149265 A (publication date: May 27, 2004) Japanese Patent Laid-Open No. 3-101769 (Publication date: April 26, 1991) JP-A-9-068874 (publication date: March 11, 1997)

  However, today, when the particle diameter of the toner has been reduced as described above, there is a problem that has not been heretofore, that is, a phenomenon in which the rear end of the image formed on the paper is retracted, It has been found that the margin set at the trailing edge of the paper is completely eliminated. It has been found that such a phenomenon that the rear end of the image moves backward is related to the printing rate on the paper and occurs when the printing rate is high.

  As a result of the inventors' efforts to investigate the cause of such a phenomenon, the paper conveyed at the transfer nip portion is caused by the phenomenon of sliding with respect to the photoreceptor, and the cause of this slipping is ( 1) Reduction in toner particle size, (2) Difference in peripheral speed between photoconductor and transfer roller, and (3) Wrinkled portion of the paper formed just before the transfer nip portion is a result of complex entanglement. There was found.

  In other words, with today's reduction in toner particle size, if the amount of toner intervening between the paper and the photoconductor is large, the adsorption force between the paper and the photoconductor is reduced. The nip pressure of the transfer nip portion does not overcome the paper feeding action by the wrinkle portion formed immediately before the transfer nip portion, and the paper is moved depending on the peripheral speed of the transfer roller, and the paper is transferred to the photosensitive member. It will slide against.

  Here, with reference to FIGS. 10 (a) and 10 (b), a mechanism by which the attractive force between the paper and the photoreceptor is reduced will be described. FIGS. 10A and 10B show the state of the transfer nip portion where the toner image is transferred. FIG. 10A shows the conventional large particle size toner T, and FIG. Is the one using today's small particle size toner t.

  In the transfer nip portion 127, the photosensitive member 121 and the transfer roller 125 are pressed from the photosensitive member 121 side through the toner (T · t) and the paper P, and the transfer voltage applying unit 129 from the transfer roller 125 side. A transfer voltage is applied. The paper P is transported in the paper transport direction indicated by the arrow X by each rotational force of the photoconductor 121 and the transfer roller 125. In the drawing, the arrow Y indicates the rotation direction of the photosensitive member 121, and the arrow Z indicates the rotation direction of the transfer roller 125.

  The toner on the photoconductor 121 is attracted to the paper P when a transfer electric field from the transfer roller 125 is applied through the paper P. As shown in FIGS. Even if the layer thickness is the same, in the case of the toner layer of the small particle size toner t, the air layer in the toner layer is larger than the toner layer of the large particle size toner T.

  Therefore, the transmission distance of the electric field between the photoconductor / toner / paper / transfer roller is longer in the toner layer of the small particle size toner t than in the toner layer of the large particle size toner T. If the transmission distance of the electric field is increased, the strength (electric field strength) is reduced when propagating through the toner layer and reaching the photosensitive member 121, and the adsorption force between the paper P and the photosensitive member 121 is reduced. .

  As described above, the suction force between the sheet and the photosensitive member is reduced, and as described above, the sheet slides with respect to the photosensitive member due to the feeding operation of the sheet deflection portion formed immediately before the transfer nip portion. A phenomenon occurs, and a phenomenon occurs in which the rear end of the image transferred to the paper P moves backward.

  If the trailing edge of the image moves backward and the margin set at the trailing edge of the paper disappears completely, there will be no printing smears or margins during subsequent printing due to toner remaining without being transferred onto the photoreceptor. In addition to the problem of quality degradation in print quality (image quality), in recent image forming devices that employ double-sided printing with a compact design and adopting the switchback transport method, paper jams occur due to paper wrapping around the fixing roller ( JAM).

  In other words, in the switchback conveyance method, the front and rear ends of the paper are reversed in the first side printing during the second side printing, so that the rear end of the paper in the first side printing is the second side printing. The leading edge of the paper. When the margin at the leading edge of the paper disappears, the paper is transported to the fixing process, which is the next process of the transfer process, and when the unfixed toner is melted and fixed, the molten toner adheres to the fixing roller, and the paper is It gets caught in the fixing roller and causes a paper jam.

  This problem that has been manifested as the particle diameter of the toner has been made small is a new problem that has not been paid attention to in the past. Of course, the technique described in the above cannot be solved.

  The present invention has been made in view of the above problems, and its purpose is to avoid the occurrence of a phenomenon that the paper slides with respect to the photosensitive member with a very simple configuration while minimizing deterioration in image quality. An object of the present invention is to provide an image forming apparatus, a control program for the image forming apparatus, and a recording medium that can ensure a margin formed at the trailing edge of the sheet.

  In order to solve the above problems, an image forming apparatus according to the present invention forms an electrostatic latent image based on image information on an electrostatic latent image carrier, and visualizes the electrostatic latent image with a developer. In the image forming apparatus in which the visible image is transferred to the recording material using the transfer unit at the transfer nip portion while the recording material is conveyed to the recording material, the visible image is disposed immediately before the transfer nip portion. A recording material conveying roller unit that conveys the recording material to the transfer nip, and a roller unit control unit that intermittently rotationally drives the recording material conveying roller unit to align the position of the recording material and the visible image The roller section control means stops the recording material conveying roller section when the leading edge of the recording material reaches the transfer nip section.

  According to this, when the roller unit control means intermittently rotationally drives the recording material conveyance roller unit to align the position of the recording material and the visible image formed on the electrostatic latent image carrier, the transfer unit When the leading edge of the recording material reaches the nip portion, the recording material conveying roller portion is stopped, so that the recording material is just before the transfer nip portion, which is one of the causes of the slip phenomenon that the recording material slides against the electrostatic latent image carrier. The recording material is not formed.

  As a result, the above-mentioned slip phenomenon does not occur in the transfer nip portion, and a defect due to a decrease or disappearance of the margin at the trailing edge of the recording material, for example, a developer that remains without being transferred onto the electrostatic latent image carrier. It is possible to reliably avoid printing contamination due to subsequent printing, degradation of printing quality (image quality) due to no margins, and paper jams at the fixing unit during double-sided printing using the switchback transport method. it can.

  The wrinkle portion formed immediately before the transfer nip portion avoids the reverse transfer phenomenon of the developer due to the recording material being adsorbed and excessively charged by the transfer means before reaching the transfer nip portion. It is necessary for the toner particle size to be small as described above. By doing so, the slip phenomenon can be achieved with a very simple configuration (control) even if the image quality is slightly sacrificed. This problem can be solved by eliminating the margin of the trailing edge of the recording material.

  The inventors of the present application also considered a configuration in which the above-described slip phenomenon is not generated by aligning the peripheral speed of the electrostatic latent image carrier with the peripheral speed of the transfer roller as a transfer unit. Since the deterioration of the print quality due to the influence of the peeling discharge generated when the material passes through the transfer nip portion was significantly larger than the decrease of the print quality when the warp portion was not formed, the configuration was made such that the warp portion was eliminated.

  In such an image forming apparatus, the transfer unit includes a transfer roller disposed in pressure contact with the latent electrostatic image bearing member via a recording material, and the transfer roller has a polarity opposite to the charging polarity of the developer. A structure to which an electric field is applied is suitable. Further, the peripheral speed of the electrostatic latent image carrier is V1 (mm / sec), the peripheral speed of the transfer roller is V2 (mm / sec), and the peripheral speed of the recording material conveyance roller disposed immediately before the transfer nip is V3. (Mm / sec), it is suitable that the above V1, V2, and V3 satisfy the relationship of V1 <V2≈V3. Furthermore, the above V1, V2, and V3 satisfy V1 × 1.005 ≦ V2≈. It is suitable to satisfy the relationship of V3 ≦ V1 × 1.03.

  That is, when the peripheral speeds of the electrostatic latent image carrier, the transfer roller, and the recording material transport roller, including the configuration of the transfer means, are in the relationship as described above, recording is performed on the electrostatic latent image carrier. Since the phenomenon that the material slips easily occurs, it is more effective to apply the invention in such a configuration. Furthermore, in terms of the ease of occurrence of the phenomenon that the recording material slides with respect to the electrostatic latent image carrier, the average particle diameter of the developer used is 7Φμm (the particle diameter of coarse powder is less than 10Φμm) or less. It is suitable to be applied to configurations that are ranges.

  In the image forming apparatus, the recording material conveying roller unit may be configured by a roller pair in which a driving roller and a driven roller are paired.

  When the drive of the recording material conveyance roller unit is stopped, the recording material passes through the recording material conveyance roller unit so as to be pulled by the conveyance force of the transfer nip portion, so that the load on the recording material conveyance roller unit increases. However, the conveyance force of the recording material is reduced, and transfer misalignment or the like is caused. However, the recording material conveyance roller portion has such a roller pair structure including a driving roller and a driven roller, so that the load is extremely large. An increase can be avoided.

  In the image forming apparatus, the roller control unit further detects the arrival of the leading end of the recording material at the transfer nip portion based on the time from the resumption of rotational driving of the recording material conveying roller unit. You can also

  The recording material conveyance roller unit is intermittently rotated to align the position of the recording material and the visible image on the electrostatic latent image carrier, and when the recording material is conveyed to the recording material conveyance roller unit. The recording material is temporarily stopped to stop the recording material, and the rotation driving is resumed at the timing when the visible image on the electrostatic latent image carrier passes through the transfer nip portion, and the recording material is conveyed to the transfer nip portion. Therefore, it is determined whether or not the leading edge of the recording material has reached the transfer nip portion from the elapsed time from when the rotational driving of the recording material conveyance roller portion was resumed to convey the recording material to the transfer nip portion. can do.

  Accordingly, it is possible to detect the arrival of the leading end of the recording material at the transfer nip portion with a smaller number of members compared to a configuration in which a sensor for detecting the passage of the leading end of the recording material is separately provided in the transfer nip portion.

  As described above, the control program for the image forming apparatus according to the present invention is a control program for causing the computer to execute the roller unit control means in the image forming apparatus according to the present invention. Defects caused by reduction or disappearance of the margin at the rear end, for example, print stains at the time of subsequent printing due to the developer remaining without being transferred onto the electrostatic latent image carrier, and print quality due to the absence of the margin ( An image forming apparatus according to the present invention capable of appropriately avoiding a paper jam at the fixing unit during double-sided printing employing a switchback conveyance method, with a simple configuration, is realized in a computer. Can be possible. Therefore, this image forming apparatus can be general purpose.

  As described above, the recording medium of the present invention is a computer-readable recording medium that records the control program for the image forming apparatus of the present invention. Troubles due to loss or loss, for example, printing stain due to developer remaining without being transferred onto the electrostatic latent image carrier, print quality deterioration (image quality) due to lack of margins, switch It is possible to easily supply a computer with a control program for an image forming apparatus according to the present invention, which can appropriately avoid a paper jam at a fixing unit during double-sided printing employing a back conveyance method. it can.

  As described above, the image forming apparatus of the present invention forms an electrostatic latent image based on image information on an electrostatic latent image carrier, and visualizes the electrostatic latent image with a developer to make a visible image. Then, in the image forming apparatus that transfers the visible image to the recording material using the transfer unit at the transfer nip portion while transporting the recording material, the transfer nip disposed immediately before the transfer nip portion. A recording material conveyance roller unit that conveys the recording material to the recording unit, and a roller unit control unit that intermittently rotationally drives the recording material conveyance roller unit in order to align the position of the recording material and the visible image, The roller section control means stops the recording material transport roller section when the leading edge of the recording material reaches the transfer nip section.

  As a result, the recording material is not formed immediately before the transfer nip, which is one of the causes of the slip phenomenon that the recording material slides on the electrostatic latent image carrier. The above-mentioned slip phenomenon does not occur and the margin at the trailing edge of the recording material decreases or disappears, for example, printing smear at the time of subsequent printing due to the developer remaining without being transferred onto the electrostatic latent image carrier. In addition, it is possible to reliably avoid the deterioration of the printing quality (image quality) due to the absence of margins, the occurrence of a paper jam at the fixing unit during double-sided printing employing the switchback conveyance method, and the like.

  The above-mentioned wrinkle part formed just before the transfer nip part is necessary to avoid the reverse transfer phenomenon of the developer due to the recording material being attracted to the transfer means and excessively charged before reaching the transfer nip part. However, today, when the particle size of the toner has been reduced as described above, slipping occurs with a very simple configuration (control) even if the image quality is slightly sacrificed. By eliminating itself, it is possible to solve the above-mentioned problem due to insufficient margin at the trailing edge of the recording material.

  An embodiment according to the present invention will be described below with reference to FIGS. Note that the present invention is not limited to this.

  As shown in FIG. 2 which is a longitudinal sectional view, the image forming apparatus according to the present embodiment includes a paper feeding unit 1, an image forming unit 2, a fixing unit 3, and a discharge unit along a paper (recording material) conveyance direction. A paper unit 4 is provided, and an image reading unit 5 is disposed above these units. Further, an optional automatic document feeder 6 is provided on the image reading unit 5. FIG. 3 shows the appearance of the image forming apparatus, and FIG. 4 shows the configuration of the image forming unit 2.

  The image reading unit 5 is provided with a document table 11 on which a document is placed, and an automatic document feeder 6 is provided to be openable and closable so as to cover the document table 11. The automatic document feeder 6 also functions as a document cover for preventing the lifted document and the like from being placed and placing the document at an appropriate position.

  The image information of the document placed on the document table 11 is read by the optical unit 12 disposed below the document table 11. The read image information is subjected to image processing in the control unit 7 and temporarily stored in a memory (not shown) as image information. The same applies to a document conveyed by the automatic document conveyance device 6, and image information is read by the optical unit 12.

  The paper feed unit 1 is provided with a paper feed cassette 13 for storing paper. The paper stored in the paper feed cassette 13 is transported to the transport path 15 as the paper feed roller 14 rotates. An idle roller (recording material conveyance roller unit) 16 is disposed in the conveyance path 15 immediately before the image forming unit 2, and the conveyance of the sheet is temporarily stopped when the leading edge of the sheet reaches the idle roller 16. Is done. The reason that the idle roller 16 stops is to align the leading edge of the image transfer area on the paper with the leading edge of the toner image visualized on the photosensitive member 21 described later.

  The image forming unit 2 forms a toner image based on image information on a sheet. As shown in FIG. 4, the image forming unit 2 includes a cylindrical photosensitive member 21, and a main charger 22, a laser scanner around the cylindrical photosensitive member 21. A unit (not shown), a developing tank (developing unit) 24, a transfer roller (transfer unit) 25, a sheet peeling claw 30, a cleaning unit 26, and the like are arranged.

  The main charger 22 applies a constant voltage to the photoconductor 21 to charge the surface of the photoconductor 21 to a predetermined potential. The laser scanner unit reads image information from the memory of the control unit 7 and irradiates the photoconductor 21 with laser light modulated by the image information, whereby electrostatic force based on the image information is applied to the photoconductor 21. It forms a latent image.

  In addition to the image information of the document placed on the document table 11 read by the image reading unit 5 and the image information of the document being moved by the automatic document feeder 6, the laser scanner unit includes the image forming apparatus. An electrostatic latent image is formed on the basis of image information transmitted from each terminal device on a network (not shown) connected.

  The electrostatic latent image formed on the photosensitive member 21 is visualized by supplying toner (developer) in the developing tank 24 to the surface of the photosensitive member 21 from the developing roller, and becomes a toner image. This visualization is achieved by the toner adhering to the surface of the photoreceptor 21 in accordance with the potential contrast of the electrostatic latent image on the photoreceptor 21. A developing bias is applied to the developing roller so that the toner easily adheres to the photoreceptor 21.

  The toner image on the photosensitive member 21 is conveyed toward the transfer roller 25 as the photosensitive member 21 rotates, and the rotation of the idle roller 16 is restarted, so that the sheet is pressed between the photosensitive member 21 and the transfer roller 25. When passing through the transfer nip portion 27, the toner image is transferred to an appropriate position on the paper. A transfer voltage is applied to the transfer nip portion 27 from the transfer roller 25 by a transfer voltage applying portion 29, and the toner is adsorbed to the paper by the transfer voltage. Thereafter, the sheet is peeled off from the photoreceptor 21 by the sheet peeling claw 30 and conveyed to the next fixing step by the rotational force of the photoreceptor 21 and the transfer roller 25. Details of the transfer process will be described later.

  The toner image transferred onto the sheet is conveyed to the fixing unit 3 in the next process, and is melted and fixed on the sheet by the heat and pressure of the fixing unit. Note that the fixing unit 3 includes a heating roller and a pressure roller.

  The sheet on which the toner image is fixed is conveyed through the conveyance path 17 and is discharged onto the sheet discharge tray 20 via the sheet discharge roller 19 during single-sided printing. On the other hand, in the case of double-sided printing, when the paper passes through the paper discharge roller 19, the rear end portion of the paper is held by the paper discharge roller 19 and is temporarily stopped, and then the paper discharge roller 19 is rotated in the reverse direction. Is guided from the original transport path 17 to the sub transport path 18.

  As described above, the method of reversely transporting the paper is generally called “switchback transport”, and the sub transport path 18 is also referred to as a switchback transport path. The paper that is switched back in this way and whose front and back are reversed reaches the idle roller 16 again, and is based on image information to be printed on the rear surface (second surface) newly visualized by the image forming unit 2. The toner image is transferred / fixed on the back surface of the paper, and is discharged onto the paper discharge tray 20 via the conveyance path 17 and the paper discharge roller 19.

  Note that the above description is intended to facilitate the general electrophotographic printing procedure, the post-processing unit for multi-functionalization, the multi-stage paper feeding unit that stores various types of paper, and the separation of discharged paper. It is obvious that various devices such as a plurality of bin discharge trays are possible.

  Next, the transfer process in the image forming apparatus will be described in detail.

  Also in this image forming apparatus, for the reasons described above, the peripheral speed of the transfer roller 25 is set to be higher than the peripheral speed of the photoconductor 21, and the photoconductor is pulled by the peripheral speed difference so that the sheet is pulled. 21 is peeled off. Further, the peripheral speed of the idle roller 16 is set to be equal to that of the transfer roller 25, and the sheet conveyed from the idle roller 16 has a slightly leading edge with respect to the contact point of the transfer nip portion 27. It is designed to be conveyed toward the outer peripheral direction and guided to the transfer nip portion 27 by the rotation of the photosensitive member 21 after the front end of the sheet contacts the photosensitive member 21.

  Here, assuming that the peripheral speed of the photosensitive member 21 is V1 (mm / sec), the peripheral speed of the transfer roller 25 is V2 (mm / sec), and the peripheral speed of the idle roller 16 is V3 (mm / sec), the above V1, V2 and V3 are designed to satisfy the relationship of V1 <V2≈V3. More specifically, V2 and V3 are designed to satisfy the relationship of V1 × 1.005 ≦ V2≈V3 ≦ V1 × 1.03. Yes. By setting each peripheral speed in this way, the reverse transfer phenomenon at the time of peeling can be avoided without pulling the paper unnecessarily strongly (fast) when peeling the paper from the photoreceptor 21, and In addition, the size of the wrinkle portion 128 (see FIG. 10 (d)) formed when the rotational driving of the idle roller 16 is controlled at the same timing as the prior art can be made appropriate.

  However, as described above, the image forming apparatus has a configuration in which a sheet warp portion is formed immediately before the transfer nip portion, and the peripheral speed of the transfer roller 25 is set slightly higher than the peripheral speed of the photosensitive member 21. Then, since the toner particle diameter is reduced, a slip phenomenon occurs in which the paper slides with respect to the photoconductor 21 when a large amount of toner is interposed between the photoconductor 21 and the paper. When such a slip phenomenon occurs, the trailing edge of the toner image transferred onto the sheet is retracted, and the margin set at the trailing edge of the sheet is reduced or eliminated. For this reason, in addition to problems such as contamination due to toner remaining on the photosensitive member and a decrease in print quality (image quality) due to the absence of margins, in the case of the image forming apparatus employing the switchback conveyance method, both sides When printing on the second side during printing, problems such as a paper jam in the fixing unit 3 are caused.

  In this image forming apparatus, in order to avoid such a decrease that the margin at the rear end of the sheet decreases or disappears, the following measures are taken. That is, when the roller section control means for controlling the rotational drive of the idle roller 16 intermittently rotationally drives the idle roller 16 to align the paper and the toner image on the photosensitive member 21, conventionally the trailing edge of the paper is The stop timing of the idle roller 16 that has been stopped after being pulled out is raised to the time when the leading edge of the paper reaches the transfer nip portion 27, and the idle roller 16 is stopped when the leading edge of the paper reaches the transfer nip portion 27. It is like that.

  As described above, when the leading edge of the paper reaches the transfer nip portion 27, the rotation of the idle roller 16 is stopped, so that the transfer, which is one of the causes of the slip phenomenon that the paper slides with respect to the photosensitive member 21, is performed. A sheet warp portion formed immediately before the nip portion 27 is not formed, and the slip phenomenon itself does not occur. As a result, the margin at the rear end of the sheet is ensured, and the above-described problems caused by the decrease or disappearance of the margin at the rear end of the sheet can be appropriately avoided.

  Further, in the case where the driving of the idle roller 16 is stopped before the trailing edge of the sheet comes off, the sheet passes through the idle roller 16 so as to be pulled by the transfer force of the transfer nip portion. Part is loaded. Such a load reduces the conveyance force of the paper and causes a transfer deviation or the like.

  Therefore, in this image forming apparatus, in order to reduce such a load as much as possible, the idle roller 16 is constituted by a roller pair in which a driving roller and a driven roller are paired. Thereby, it can avoid that load increases extremely.

  Here, the roller unit control means is realized by the CPU 31, the ROM 32, and the RAM 33 provided in the control unit 7 shown in FIG. The control unit 7 of the image forming apparatus will be described with reference to FIG. FIG. 1 is a block diagram illustrating a configuration of the control unit 7 of the image forming apparatus.

  The CPU 31 is a central part that controls all operations of the image forming apparatus. In other words, the image information transmitted from the terminal device and the image information read by the image reading unit 5 are received from the image information input unit, and are input from the operation unit such as the condition input unit or the display unit. The image information processing unit 34 processes image information in accordance with an instruction such as a print request.

  Then, the image information subjected to the image processing is sent to the print processing unit, and the laser scanner unit, the print process unit for controlling the image forming unit 2, the fixing control unit for controlling the fixing unit 3, and the discharge unit for controlling the paper discharge unit 4. In addition to controlling the paper control unit and the like, and controlling the paper conveyance system such as the paper feeding unit 1 and the idle roller 16 via the paper conveyance control unit 34, an image is formed on the instructed predetermined size paper P. . In addition, the CPU 31 also controls optional devices such as the automatic document feeder 6 via the optional processing unit.

  The image information processing unit, as an image processing unit, receives an input image processing unit that performs predetermined image processing on image information input through the image information input unit, and image data processed by the input image processing unit. An output image processing unit that performs predetermined image processing to form output image data for forming a writing image to be output to the print processing unit.

  In this image forming apparatus, the CPU 31 controls the rotation of the idle roller 16 via the paper conveyance control unit 34, and conventionally, the idle roller that has been stopped after the trailing edge of the paper passes through the idle roller 16 is stopped. 16 is pulled up so that it stops when the leading edge of the paper reaches the transfer nip 27.

  Further, the CPU 31 detects the confirmation of the arrival of the leading edge of the sheet at the transfer nip portion based on the time from the resumption of the rotational driving of the idle roller 16. As described above, the rotational driving of the idle roller 16 is temporarily stopped when the leading edge of the paper reaches the idle roller 16 in order to align the position of the paper and the toner image on the photoconductor 21. Since the toner image is restarted in accordance with the timing when the toner image passes through the transfer nip portion 27, the elapsed time from the time when the rotational driving of the idle roller 16 is restarted to transport the recording material to the transfer nip portion 27. Thus, it can be determined whether or not the leading edge of the sheet has reached the transfer nip portion 27. Such a detection method determines whether or not the leading edge of the paper has reached the transfer nip portion 27 with a small number of members, compared to a configuration in which a sensor for detecting passage of the leading edge of the paper is separately provided in the transfer nip portion 27. Can be detected.

  The ROM 32 stores various programs used by the CPU 31 for causing the image forming apparatus to function and data such as the number of steps of the motor, including the function as the roller unit control unit described above. The RAM 33 is a storage unit (memory) used by the CPU 31.

  FIG. 5 shows the timing of voltage application to the photoreceptor 21, the transfer nip portion 25, the idle roller 16, the paper transport path, and the transfer roller 25 in the image forming apparatus. FIG. 6 shows the timing of voltage application to the photoconductor, transfer nip, idle roller, paper transport path, and transfer roller in a conventional image forming apparatus.

  The timing for starting (resuming) the rotation of the idle roller 16 is the same for both the image forming apparatus and the conventional image forming apparatus. This is the timing at which the leading edge of the image forming position is synchronized on the paper.

  On the other hand, the timing at which the rotation of the idle roller 16 is stopped is the timing at which the trailing edge of the sheet passes through the idle roller in the conventional image forming apparatus, but in this image forming apparatus, the leading edge of the sheet is the transfer nip. It is the time when the part 27 is reached.

  Note that since it is not necessary to form a wrinkle portion that is a problem, it is not necessary that the leading edge of the sheet reaches the transfer nip portion 27, and even if there is no conveying force of the idle roller 16, the conveying force of the transfer nip portion 27. As long as the sheet can be conveyed by the sheet, it is sufficient that the sheet is caught in the transfer nip portion 27.

  FIGS. 7A to 7E show how the paper P is conveyed to the transfer nip portion 27 in the image forming apparatus. The toner image 10 formed on the photoconductor 21 is conveyed to the transfer nip portion 27 by the rotation of the photoconductor 21, and the paper P is conveyed to the transfer nip portion 27 by the rotation of the idle roller 16. The paper P transported from the idle roller 16 is transported by the guide of the paper guide 40 so that the front end thereof is slightly directed toward the outer peripheral direction of the photoreceptor 21 with respect to the contact point of the transfer nip portion 27. As a result, the paper P is brought into contact with the photoconductor 21 and then guided to the transfer nip portion 27 by the rotation of the photoconductor 21. By controlling the timing of resuming the rotation of the idle roller 16 with respect to the photoconductor 21 of the paper P, the leading edge of the toner image 10 and the leading edge of the image forming area of the paper P (the margin at the leading edge rather than the leading edge of the paper) The contact is made in a state where the tip of the removed area matches.

  When the leading edge of the paper P reaches the transfer nip portion 27, the rotational driving of the idle roller 16 is stopped, and the paper P is transported by the transport force of the transfer nip portion 27. When the rotational driving of the idle roller 16 is stopped, the sheet P does not bend immediately before the transfer nip portion 27, and a warp portion is not formed. The leading end portion of the paper P onto which the toner image 10 has been transferred through the transfer nip portion 27 is peeled off from the photoreceptor 21 by the paper peeling claw 30 and conveyed along the paper guide 41.

  Next, the rotational driving of the idle roller 16 during the image forming operation by the image forming apparatus having such a configuration will be described with reference to the flowchart of FIG.

  When the sheet P is fed and conveyed from the sheet feeding unit 1 (S1), the CPU 31 determines whether or not the leading end of the conveyed sheet P has reached the idle roller 16 (S2), and determines that it has arrived. Then, the rotational driving of the idle roller 16 is temporarily stopped (S3).

  Thereafter, the CPU 31 determines whether or not the timing at which the leading edge of the toner image 10 formed by developing the electrostatic latent image formed on the photosensitive member 21 coincides with the leading edge of the image writing position on the paper P is reached. If it is determined that the timing is reached (S4), the rotational driving of the idle roller 16 is resumed (S5). As a result, the conveyance of the sheet P stopped at the idle roller 16 is resumed, and the leading edge of the sheet P is guided to the transfer nip portion 27.

  Subsequently, the CPU 31 determines whether or not the leading edge of the sheet P has reached the transfer nip portion 27, that is, whether or not the leading edge of the sheet P is sandwiched between the transfer roller 25 and the photosensitive member 21 (S6). Is determined to be clamped, the rotational driving of the idle roller 16 is stopped (S7).

  As described above, in this image forming apparatus, the stop timing of the idle roller 16 is advanced to prevent the occurrence of the phenomenon that the image extends on the paper P due to the slip of the paper P, causing the image to extend. Since the sheet P is not bent immediately before the transfer nip portion 27 that causes the slip phenomenon, the slip that slides on the sheet P photoconductor 21 with a very simple configuration while suppressing deterioration in image quality as much as possible. Occurrence of the phenomenon can be eliminated, the margin formed at the rear end portion of the sheet can be ensured, and the above-described problems caused by the decrease or disappearance of the white can be appropriately avoided.

  The roller control unit in the image forming apparatus may be realized by hardware logic, or may be realized by software using a CPU as described in the present embodiment.

  That is, a CPU (central processing unit) that executes instructions of an image processing method that realizes a function as a roller unit control means, a ROM (read only memory) that stores the program, a RAM (random access memory) that expands the program, A storage device (recording medium) such as a memory for storing the program and various data is provided. Then, the image forming apparatus supplies the image reading apparatus with a recording medium in which the program code (execution format program, intermediate code program, source program) of the reading area control program for realizing the functions described above is recorded so as to be readable by the computer. This can also be realized by reading and executing the program code recorded on the recording medium by the computer (or CPU or MPU). In this case, the program code itself read from the recording medium realizes the above-described function, and the recording medium recording the program code constitutes the present invention.

  Thus, in this specification, the means (unit) does not necessarily mean a physical means, but includes cases where the function of each means is realized by software. Further, the function of one means may be realized by two or more physical means, or the functions of two or more means may be realized by one physical means.

  In the present embodiment, as the recording medium, a memory (not shown) such as a ROM itself may be a program medium because processing is performed by a microcomputer. However, it may be a program medium provided with a program reading device as an external storage device and readable by inserting a recording medium therein.

  In any case, the stored program may be configured to be accessed and executed by the microprocessor, or in any case, the program is read and the read program is illustrated in the microcomputer. The program may be downloaded to a non-program storage area and executed. It is assumed that this download program is stored in the main device in advance.

  Here, the program medium is a recording medium configured to be separable from the main body, such as a tape system such as a magnetic tape or a cassette tape, a magnetic disk such as a floppy (registered trademark) disk or a hard disk, or a CD-ROM / MO /. MD / DVD optical discs, IC cards (including memory cards) / optical cards, etc. Mask ROM, EPROM (Erasable Programmable Read Only Memory), EEPROM (Electrically Erasable Programmable Read Only Memory), flash It may be a medium that carries a fixed program including a semiconductor memory such as a ROM.

  In the present embodiment, since the system configuration is such that a communication network including the Internet can be connected, a medium that fluidly carries the program so as to download the program from the communication network may be used. When the program is downloaded from the communication network in this way, the download program may be stored in the main device in advance or may be installed from another recording medium.

1 is a block diagram illustrating a configuration of a control unit of an image forming apparatus according to an embodiment of the present invention. It is a longitudinal cross-sectional view which shows the structure of the said image forming apparatus. It is a perspective view which shows the external appearance of the said image forming apparatus. It is explanatory drawing which shows the structure of the image formation part in the said image forming apparatus. 4 is a timing chart showing timings of driving of a photosensitive member, a transfer nip portion, an idle roller, a sheet conveyance path, and application of a voltage to a transfer roller in the image forming apparatus. 6 is a timing chart showing timings of driving of a photosensitive member, a transfer nip portion, an idle roller, a sheet conveyance path, and application of a voltage to a transfer roller in a conventional image forming apparatus. (A)-(e) is explanatory drawing which shows the conveyance state of the paper to the transfer nip part in the said image forming apparatus. 4 is a flowchart illustrating a control procedure for rotational driving of an idle roller in the image forming apparatus. (A)-(e) is explanatory drawing which shows the conveyance state of the paper to the transfer nip part in the conventional image forming apparatus. (A) and (b) are both explanatory views showing the mechanism of the decrease in the attractive force between the photosensitive member and the paper accompanying the reduction in the toner particle size.

Explanation of symbols

10 Toner image (visible image)
16 Idle roller (Recording material transport roller)
21 Photoconductor (electrostatic latent image carrier)
25 Transfer roller 27 Transfer nip 31 CPU (roller control means)
32 ROM (roller control means)
33 RAM (roller control means)
P paper (recording material)

Claims (6)

An electrostatic latent image based on image information is formed on the electrostatic latent image carrier, and the electrostatic latent image is visualized with toner to be a visible image, and then the visible image is recorded on the recording material. In an image forming apparatus that transfers using a transfer means at a transfer nip while conveying a material,
The transfer unit includes a transfer roller that is disposed in pressure contact with the electrostatic latent image carrier via a recording material and to which an electric field having a polarity opposite to the charging polarity of the toner is applied.
Immediately before the transfer nip portion, a recording material conveyance roller portion for conveying a recording material to the transfer nip portion is provided, and the recording material conveyance roller is configured to align the recording material and the visible image. Driven intermittently by the roller control means,
The toner has an average particle size of 7 μm or less,
When the peripheral speed of the electrostatic latent image carrier is V1 (mm / sec), the peripheral speed of the transfer roller is V2 (mm / sec), and the peripheral speed of the recording material transport roller is V3 (mm / sec), V1, V2, and V3 satisfy the relationship of V1 <V2≈V3,
Furthermore, the roller unit control means, the image forming apparatus characterized by being adapted to stop the rotation of the recording material conveyance roller unit when the leading end of the recording material has reached the transfer nip portion. V1, V2, and V3 are
The image forming apparatus according to claim 1 , wherein a relationship of V1 × 1.005 ≦ V2≈V3 ≦ V1 × 1.03 is satisfied. 3. The image forming apparatus according to claim 1, wherein the recording material conveying roller section is configured by a roller pair in which a driving roller and a driven roller are paired. The roller unit control means, to reach the transfer nip portion at the distal end of the recording material, any請Motomeko 1 to 3, wherein the detecting the time from the rotation drive resumption of the recording material conveyance roller unit whether the image forming apparatus according to (1).   5. A control program for an image forming apparatus for causing a computer to execute the roller unit control means in the image forming apparatus according to claim 1.   A computer-readable recording medium on which the control program for the image forming apparatus according to claim 5 is recorded.

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